Seating unit including novel back construction

ABSTRACT

A back construction for a seating unit includes a back frame, and a compliant back having a forwardly-protruding lumbar support section that is characteristically flexible and bendable, such that the compliant back can be flexed to a plurality of different convex shapes. Top and bottom connections pivotally connect the compliant back to the back frame. An adjustable force-generating mechanism is operably attached to at least one of the compliant back and the back frame. The force-generating mechanism is constructed to provide an adjustable biasing force that adjustably biases the lumbar support section forwardly for optimal lumbar support for a seated user&#39;s back, but the force-generating mechanism characteristically provides the biasing force without forcing a shape change in the compliant back. A vertically adjustable lumbar support is slidably attached to the back shell.

BACKGROUND

[0001] The present invention concerns seating units having a reclineableback, and more particularly concerns seating units having a reclineableback and a forwardly movable/tiltable seat that moves with a synchronousmovement as the back is reclined.

[0002] Manufacturers are becoming increasingly aware that adequatelumbar support is important to prevent lower back discomfort anddistress in workers who are seated for long periods. A problem is thatthe spinal shape and body shape of workers vary tremendously, such thatit is not possible to satisfy all workers with the same shape. Further,the desired level of firmness or force of support in the lumbar area isdifferent for each person and may vary as a seated user performsdifferent tasks and/or reclines in the chair and/or becomes fatigued. Infact, a static lumbar support is undesirable. Instead, it is desirableto provide different lumbar shapes and levels of support over a workday. Merely providing a particular shape or an adjustable lumbar supportis not enough since seated users are constantly changing their positionin the chair. Instead, the chair back must move and flex in asympathetic manner that mirrors the movement of a human spine and lowerback while providing good postural support in all body positions.Accordingly, an adjustable lumbar system is desired that is constructedto widely vary the shape and force of lumbar support. At the same time,the adjustable lumbar system must be simple and easy to operate, easilyreached while seated, mechanically non-complex and low cost, andaesthetically/visually pleasing. Preferably, adjustment of the shapeand/or force in the lumbar area should not result in wrinkles in thefabric of the chair, nor unacceptable loose/saggy patches in the fabric,even while the range of shape and force adjustment is increased.

[0003] A synchrotilt chair is described in U.S. Pat. No. 5,050,931 (toKnoblock) having a base assembly with a control, a reclineable backpivoted to the control, and a seat operably mounted to the back andcontrol for synchronous motion as the back is reclined. This prior artchair incorporates a semi-rigid flexible shell that, in combination withthe chair support structure, provides a highly-controlled posturalsupport during the body movements associated with tasks/work (e.g., whenthe back is in an upright position) and during the body movementsassociated with recline/relaxation (e.g., when the chair is in areclined position). This prior art chair moves a seated user's upperbody away from the user's work surface as the user reclines, thusproviding the user with more area to stretch. In fact, moving around ina chair and not staying in a single static position is important to goodback health in workers whose jobs require a lot of sitting.

[0004] However, users often want to remain close to their work surfaceand want to continue to work at the work surface, even while recliningand relaxing their body and while having continued good posturalsupport.

[0005] Modern customers and chair purchasers also demand a wide varietyof chair options and features, and a number of options and features areoften designed into chair seats. However, improvement in seats isdesired so that a seated user's weight is adequately supported on thechair seat, but simultaneously so that the thigh area of a seated useris comfortably, adjustably supported in a manner that adequately allowsfor major differences in the shape and size of a seated user's buttocksand thighs. Additionally, it is important that such options and featuresbe incorporated into the chair construction in a way that minimizes thenumber of parts and maximizes the use of common parts among differentoptions, maximizes efficiencies of manufacturing and assembling,maximizes ease of adjustment and the logicalness of adjustment controlpositioning, and yet that results in a visually pleasing design.

[0006] Accordingly, a chair construction solving the aforementionedproblems is desired.

SUMMARY OF INVENTION

[0007] In another aspect on the present invention, a back constructionfor a seating unit includes a back frame, and a compliant back having aforwardly-protruding lumbar support section that is characteristicallyflexible and bendable, such that the compliant back can be flexed to aplurality of different convex shapes. Top and bottom connectionspivotally connect the compliant back to the back frame. An adjustableforce-generating mechanism is operably attached to at least one of thecompliant back and the back frame. The force-generating mechanism isconstructed to provide an adjustable biasing force that adjustablybiases the lumbar support section forwardly for optimal lumbar supportfor a seated user's back, but the force-generating mechanismcharacteristically provides the biasing force without forcing a shapechange in the compliant back.

[0008] In another aspect on the present invention, a seating unitincluding a base assembly having a control housing having an energysource therein, and a back assembly movably supported on the baseassembly. The base assembly includes a back support operablyinterconnected to the energy source. The back support includes a backframe and a back shell connected to the back frame by at least oneconnection. The back shell includes a resiliently flexible polymericsheet adapted to support a back of a seated user. The sheet includes alower area disposed generally in a pelvic area on the seating unit, acentral area disposed above the lower area and generally in a lumbararea on the seating unit, and an upper area disposed above the centralarea and generally in a thoracic area on the seating unit. A cushion isprovided on a forward face of the back shell. A vertically adjustablelumbar support is located in front of the back shell. The lumbar supportis movably supported on the back support and configured for verticaladjustment to change a shape of a front surface of the back in thelumbar area. The vertically adjustable lumbar support includes laterallyextending handles constructed to engage and follow configurednon-parallel opposing perimeter edges of the back shell and constructedto slidably engage the vertically adjustable lumbar support to permitthe handles to adjust laterally in and out to follow the perimeteredges.

[0009] These and other features and advantages of the present inventionwill be further understood and appreciated by those skilled in the artby reference to the following specification, claims, and appendeddrawings.

DESCRIPTION OF FIGURES

[0010] FIGS. 1-3 are front, rear, and side perspective views of areclineable chair embodying the present invention;

[0011]FIGS. 4A and 4B are exploded perspective views of upper and lowerportions of the chair shown in FIG. 1;

[0012]FIGS. 5 and 6 are side views of the chair shown in FIG. 1, FIG. 5showing the flexibility and adjustability of the chair when in theupright position and FIG. 6 showing the movements of the back and seatduring recline;

[0013]FIG. 7 is a front view of the chair shown in FIG. 1 with anunderseat aesthetic cover removed;

[0014]FIG. 8 is a top view of the control including the primary energymechanism, the moment arm shift adjustment mechanism, and the back-stopmechanism, the primary energy mechanism being adjusted to a relativelylow torque position and being oriented as it would be when the back isin the upright position so that the seat is in its rearward at-restposition, the back-stop mechanism being in an intermediate position forlimiting the back to allow a maximum recline;

[0015]FIG. 8A is a perspective view of the base frame and the chaircontrol shown in FIG. 8, some of the seat and back support structurebeing shown in phantom lines and some of the controls on the controlbeing shown in solid lines to show relative locations thereof;

[0016]FIG. 9 is a perspective view of the control and primary energymechanism shown in FIG. 8, the primary energy mechanism being adjustedto a low torque position and shown as if the back is in an uprightposition such that the seat is moved rearwardly;

[0017]FIG. 9A is a perspective view of the control and primary energymechanism shown in FIG. 9, the primary energy mechanism being adjustedto the low torque position but shown as if the back is in a reclinedposition such that the seat is moved forwardly and the spring iscompressed;

[0018]FIG. 9B is a perspective view of the control and primary energymechanism shown in FIG. 9, the primary energy mechanism being adjustedto a high torque position and shown as if the back is in an uprightposition such that the seat is moved rearwardly;

[0019]FIG. 9C is a perspective view of the control and primary energymechanism shown in FIG. 9, the primary energy mechanism being adjustedto the high torque position but shown as if the back is in a reclinedposition such that the seat is moved forwardly and the spring iscompressed;

[0020]FIG. 9D is a graph showing torsional force versus angulardeflection curves for the primary energy mechanism of FIGS. 9-9C, thecurves including a top curve showing the forces resulting from the hightorque (long moment arm engagement of the main spring) and a bottomcurve showing the forces resulting from the low torque (short moment armengagement of the main spring);

[0021]FIG. 10 is an enlarged top view of the control and primary energymechanism shown in FIG. 8, including controls for operating theback-stop mechanism, the back-stop mechanism being shown in an offposition;

[0022]FIG. 11 is an exploded view of the mechanism for adjusting theprimary energy mechanism, including the overtorque release mechanism forsame;

[0023]FIG. 11A is a plan view of a modified back-stop control andrelated linkages; FIG. 11B is an enlarged fragmentary view, partially incross-section, of the circled area in FIG. 11A; and Fig. 11C is across-sectional view taken along the line XIC-XIC in FIG. 11A;

[0024]FIG. 12 is a side view of the back assembly shown in FIG. 1including the back frame and the flexible back shell and including theskeleton and flesh of a seated user, the back shell being shown with aforwardly-convex shape in solid lines and being shown in differentflexed shapes in dashed and dotted lines;

[0025]FIG. 12A is an enlarged perspective view of the back frame shownin FIG. 4A, the back frame being shown as if the molded polymeric outershell is transparent so that the reinforcement can be easily seen;

[0026]FIGS. 12B and 12C are cross-sections taken along lines XXIIB-XXIIBand XXIIC-XXIIC in FIG. 12A;

[0027] FIGS. 12D-12I are views showing additional embodiments offlexible back shell constructions adapted to move sympathetically with aseated user's back;

[0028]FIG. 12J is an exploded perspective view of thetorsionally-adjustable lumbar support spring mechanism shown in FIG. 4A,and FIG. 12JJ is an exploded view of the hub and spring connection ofFIG. 12J taken from an opposite side of the hub;

[0029]FIG. 12K is an exploded perspective view of a modifiedtorsionally-adjustable lumbar support spring mechanism;

[0030] FIGS. 12L and 12LL are side views of the mechanism shown in FIG.12K adjusted to a low torque position, and FIGS. 12M and 12MM are sideviews of the mechanism adjusted to a high torque position, FIGS. 12L and12M highlighting the spring driver, and FIGS. 12LL and 12MM highlightingthe lever;

[0031]FIG. 12N is a fragmentary cross-sectional side view of the backconstruction shown in FIG. 12;

[0032]FIG. 13 is a cross-sectional side view taken along lines XIII-XIIIshowing the pivots that interconnect the base frame to the back frameand that interconnect the back frame to the seat frame;

[0033]FIG. 13A is a cross-sectional side view of modified pivots similarto FIG. 13, but showing an alternative construction;

[0034]FIGS. 14A and 14B are perspective and front views of the topconnector connecting the back shell to the back frame;

[0035]FIG. 15 is a rear view of the back shell shown in FIG. 4A;

[0036]FIG. 16 is a perspective view of the back including thevertically-adjustable lumbar support mechanism shown in FIG. 4A;

[0037]FIGS. 17 and 18 are front and top views of thevertically-adjustable lumbar support mechanism shown in FIG. 16;

[0038]FIG. 19 is a front view of the slide frame of thevertically-adjustable lumbar support mechanism shown in FIG. 18;

[0039]FIG. 20 is a top view, partially in cross-section, of thelaterally-extending handle of the vertically-adjustable lumbar supportmechanism shown in FIG. 17 and its attachment to the slide member of thelumbar support mechanism;

[0040]FIG. 21 is a perspective view of the depth-adjustable seat shownin FIG. 4B including the seat carrier and the seat undercarriage/supportframe slidably mounted on the seat carrier, the seatundercarriage/support frame being partially broken away to show thebearings on the seat carrier, the seat cushion being removed to revealthe parts therebelow;

[0041]FIG. 22 is a top view of the seat carrier shown in FIG. 21, theseat undercarriage/rear frame being removed but the seat frame slidebearings being shown and the seat carrier depth-adjuster stop devicebeing shown;

[0042]FIG. 23 is a top perspective view of the seat undercarriage/rearframe and the seat carrier shown in FIG. 21 including a depth-adjustercontrol handle, a linkage, and a latch for holding a selected depthposition of the seat;

[0043]FIGS. 24 and 25 are side views of the depth-adjustable seat shownin FIG. 21, FIG. 24 showing the seat adjusted to maximize seat depth,and FIG. 25 showing the seat adjusted to minimize seat depth; FIGS. 24and 25 also showing a manually-adjustable “active” thigh support systemincluding a gas spring for adjusting a front portion of the seat shellto provide optimal thigh support;

[0044]FIG. 26 is a top view of the seat support structure shown in FIGS.24 and 25 including the seat carrier (shown mostly in dashed lines), theseat undercarriage/rear frame, the active thigh support system with gasspring and reinforcement plate for adjustably supporting the frontportion of the seat, and portions of the depth-adjustment mechanismincluding a stop for limiting the maximum forward and rearward depthadjustment of the seat and the depth-setting latch;

[0045]FIG. 26A is a cross-section taken along line XXVIA-XXVIA in FIG.26 showing the stop for the depth-adjuster mechanism;

[0046]FIGS. 27 and 28 are top and bottom perspective views of the seatsupport structure shown in FIG. 26;

[0047]FIGS. 29 and 30 are top and bottom perspective views of a seatsimilar to that shown in FIG. 26, but where the manually-adjustablethigh support system is replaced with a passive thigh support systemincluding a leaf spring for supporting a front portion of the seat; and

[0048]FIG. 31 is a bottom perspective view of the brackets and guide forsupporting ends of the leaf spring as shown in FIG. 30, but with thethigh-supporting front portion of the seat flexed downwardly causing theleaf spring to flex toward a flat compressed condition.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0049] For purposes of description herein, the terms “upper,” “lower,”“right,” “left,” “rear,” “front,” “vertical,” “horizontal,” andderivatives thereof shall relate to the invention as oriented in FIG. 1with a person seated in the chair. However, it is to be understood thatthe invention may assume various alternative orientations, except whereexpressly specified to the contrary. It is also to be understood thatthe specific devices and processes illustrated in the attached drawingsand described in the following specification are simply exemplaryembodiments of the inventive concepts defined in the appended claims.Hence, specific dimensions and other physical characteristics relatingto the embodiments disclosed herein are not to be considered asunnecessarily limiting, unless the claims expressly state otherwise.

[0050] A chair construction 20 (FIGS. 1 and 2) embodying the presentinvention (sometimes referred to herein as a “seating unit”) includes acastored base assembly 21 and a reclineable back assembly 22 pivoted tothe base 21 for movement about a stationary back-tilt axis 23 betweenupright and reclined positions. A seat assembly 24 (FIG. 6) is pivotedat its rear to the back 22 for movement about a seat-tilt axis 25.Seat-tilt axis 25 is offset rearwardly and downwardly from the back-tiltaxis 23, and the seat 24 is slidably supported at its front on the base21 by linear bearings, such that the seat 24 slides forwardly and itsrear rotates downwardly and forwardly with a synchrotilt movement as theback 22 is reclined (see FIG. 6). The synchronous motion initially movesthe back to seat at an angular synchronous ratio of about 2.5:1, andwhen near the fully reclined position moves the back to seat at anangular synchronous ratio of about 5:1. The seat 24 and back 22 movementduring recline provides an exceptionally comfortable ride that makes theseated user feel stable and secure. This is due in part to the fact thatthe movement keeps the seated user's center of gravity relativelyconstant and keeps the seated user in a relatively balanced positionover the chair base. Also, the forward slide/synchronous motion keepsthe seated user near his/her work during recline more than in previoussynchrotilt chair constructions, such that the problem of constantlyscooting forward after reclining and then scooting rearward when movingtoward an upright position is greatly reduced, if not eliminated.Another advantage is that the chair construction 20 can be used close toa wall behind the chair or in a small office, with less problemsresulting from interference from office furnishings during recline.Still further, we have found that the spring 28 for biasing the back 22toward an upright position can be potentially reduced in size because ofthe reduced rearward shifting of a seated user's weight in the presentchair.

[0051] The base 21 includes a control housing 26. A primary energymechanism 27 (FIG. 8) is operably positioned in control housing 26 forbiasing the seat 24 rearwardly. Due to the interconnection of the back22 and the seat 24, the rearward bias of the seat 24 in turn biases theback 22 toward an upright position. Primary energy mechanism 27 (FIG. 8)includes a main spring 28 positioned transversely in the control housing26 that operably engages a torque member or lever 54. The tension andtorque provided by the main spring 28 is adjustable via an adjustablemoment arm shift (MAS) system 29 also positioned substantially in thecontrol housing 26. A visual cover 26′ (FIG. 1) covers the area betweenthe control housing 26 and the underside of the seat 24. The backassembly 22 includes a back support or back frame 30 (FIG. 4A) withstructure that defines pivots/axes 23 and 25. A flexible/compliant backshell construction 31 is pivoted to back frame 30 at top connections 32and bottom connections 33 in a manner providing an exceptionallycomfortable and sympathetic back support. A torsionally-adjustablelumbar support spring mechanism 34 is provided to bias the back shell 31forwardly into a forwardly-convex curvilinear shape optimally suited forproviding good lumbar pressure. A vertically-adjustable lumbar support35 (FIG. 16) is operatively mounted on back shell 31 for verticalmovement to provide an optimal shape and pressure location to the frontsupport surface on back 22. The seat 24 is provided with various optionsto provide enhanced chair functions, such as a back-stop mechanism 36(FIG. 8) which adjustably engages the seat 24 to limit recline of theback 22. Also, the seat 24 can include active and passive thigh supportoptions (see FIGS. 24 and 30, respectively), seat depth adjustment (seeFIGS. 28 and 25), and other seat options, as described below.

Base Assembly

[0052] The base assembly 21 (FIG. 1) includes a floor-engaging support39 having a center hub 40 and radially-extending castored legs 41attached to the center hub 40 in a spider-like configuration. Atelescopingly-extendable center post 42 is positioned in center hub 40and includes a gas spring that is operable to telescopingly extend thepost 42 to raise the height of the chair. The control housing 26 is panshaped (FIG. 11) and includes bottom panels and flanged sidewallsforming an upwardly-open structural member. A notch 43 is formed in onesidewall of the housing 26 for receiving a portion of the adjustablecontrol for the MAS system 29. A front of the housing 26 is formed intoan upwardly-facing U-shaped transverse flange 44 for receiving atransverse structural tube 45 (FIG. 8A), and a hole 46 (FIG. 11) isformed generally adjacent flange 44. The transverse tube 45 is welded tothe flange 44 and extends substantially horizontally. A reinforcementchannel 47 is welded in housing 26 of base assembly 21 immediately infront of transverse structural tube 45. A frustoconical tube section 48is welded vertically to reinforcement 47 above hole 46, which tubesection 48 is shaped to mateably and securely engage the upper end ofextendable center post 42. A pair of stiff upwardly-extending side arms49 (sometimes also called “struts” or “pods”) are welded to the opposingends of transverse tube 45. The side arms 49 each include a stiff plate50 on their inside surface. The plates 50 include weld nuts 51 thatalign to define the back-tilt axis 23.

[0053] The housing 26, transverse tube 45, and side arms 49 form a baseframe that is rigid and sturdy. The sidewalls of the housing 26 includea lip or flange that extends along their upper edge to reinforce thesidewalls. A cap 52 is attached to the lips to form a stationary part ofa linear bearing for slidably supporting a front of the seat.

Primary Energy Mechanism and Operation

[0054] It is noted that the housing 26 shown in FIGS. 9-9C and 10 isslightly longer and with different proportions than the housing of FIGS.8, 8A, and 11, but the principles of operation are the same. The primaryenergy mechanism 27 (FIG. 8) is positioned in housing 26. The primaryenergy mechanism 27 includes the spring 28, which is operably connectedto the seat 24 by an L-shaped torque member or bell crank 54, a link 55,and a seat-attached bracket 56. The spring 28 is a coil springtransversely positioned in housing 26, with one end supported against aside of housing 26 by a disc-shaped anchor 57. The anchor 57 includes awasher to support the end of the spring 28 to prevent noise, and furtherincludes a protrusion that extends into a center of the end of thespring 28 to securely grip the spring 28, but that allows the spring 28to be compressed and to tilt/flex toward a side while the torque memberor bell crank 54 is being pivoted. The L-shaped torque member or bellcrank 54 includes a short leg or lever 58 and a long leg 59. The shortleg 58 has a free end that engages an end of the spring 28 generallyproximate a left side of housing 26 with a washer and protrusion similarto anchor 57. Short leg 58 is arcuately shaped and includes an outersurface facing the adjacent sidewall of housing 26 that defines a seriesof teeth 60. Steel strips 61 are attached to the top and bottom sides ofthe short leg 58 and have an outer arcuate surface that provides asmooth rolling bearing surface on the leg 58, as described below. Thearcuate surface of the strips 61 is generally located at about the apexor the pitch diameter of the gear teeth 60. The short leg 58 extendsgenerally perpendicular to a longitudinal direction of spring 28 and thelong leg 59 extends generally parallel the length of spring 28, but isspaced from the spring 28. Link 55 (FIG. 8) is pivoted to an end of longleg 59 and is also pivoted to the seat-attached bracket 56.

[0055] A crescent-shaped pivot member 63 (FIG. 11) includes an arcuateroller bearing surface that rollingly engages the curved surface ofsteel strips 61 on short leg 58 to define a moving fulcrum point. Pivotmember 63 also includes a rack of teeth 64 configured to mateably engagethe teeth 60 on short leg 58 to prevent any slippage between theinterfacing roller bearing surfaces of leg 58 and pivot member 63. Pivotmember 63 is attached to a side of the housing 26 at the notch 43. Whenthe seat 24 is in a rearward position (i.e., the back is in an uprightposition) (FIG. 9), the long leg 59 is located generally parallel andclose to the spring 28 and the short leg 58 is pivoted so that thespring 28 has a relatively low amount of compression. In this position,the compression of spring 28 is sufficient to adequately bias the seat24 rearwardly and in turn bias the back frame 30 to an upright positionfor optimal yet comfortable support to a seated user. As a seated userreclines, the seat 24 is moved forwardly (FIG. 9A). This causes theL-shaped torque member or bell crank 54 to roll on pivot member 63 atthe fulcrum point in a manner compressing spring 28. As a result, spring28 provides increasing force resisting the recline, which increasingforce is needed to adequately support a person as they recline. Notably,the short leg 58 “walks” along the crescent-shaped pivot member 63 ashort distance during recline, such that the actual pivot locationchanges slightly during recline. The generous curvilinear shapes of theshort leg 58 and the pivot member 63 prevent any abrupt change in thesupport to the back during recline, but it is noted that the curvilinearshapes of these two components affect the spring compression in twoways. The “walking” of the short leg 58 on the pivot member 63 affectsthe length of the moment arm to the actual pivot point (i.e., thelocation where the teeth 60 and 64 actually engage at any specific pointin time). Also, the “walking” can cause the spring 28 to belongitudinally compressed as the “walking” occurs. However, in apreferred form, we have designed the system so that the spring 28 is notsubstantially compressed during adjustment of the pivot member 63, forthe reason that we want the adjustment to be easily accomplished. Ifadjustment caused the spring 28 to be compressed, the adjustment wouldrequire extra effort to perform the adjustment, which we do not preferin this chair design.

[0056] As discussed below, the pivot member 63 is adjustable to changethe torque arm over which the spring 28 operates. FIG. 9B shows theprimary energy mechanism 27 adjusted to a high torque position with theseat 24 being in a rearward position (and the back frame 30 being in anupright position). FIG. 9C shows the primary energy mechanism 27 stilladjusted to the high torque condition, but in the compressed conditionwith the seat 24 in a forward position (and the back frame 30 being inan upright position). Notably, in FIGS. 9B and 9C, the pivot member 63has been adjusted to provide a longer torque arm on lever 58 over whichthe spring 28 acts.

[0057]FIG. 9D is a graph illustrating the back torque generated byspring 28 as a function of the angle of recline. As apparent from thegraph, the initial force of support can be varied by adjustment (asdescribed below). Further, the rate of change of torsional force (i.e.,the slope) varies automatically as the initial torsional force isadjusted to a higher force, such that a lower initial spring forceresults in a flatter slope, while a higher initial spring force resultsin a steeper slope. This is advantageous since lighter/smaller peoplenot only require less support in the upright position of the chair, butalso require less support during recline. Contrastingly, heavier/largerpeople require greater support when in upright and reclined positions.Notably, the desired slope of the high and low torque force/displacementcurves can be designed into the chair by varying the shape of the shortleg 58 and the pivot member 63.

[0058] The crescent-shaped pivot member 63 (FIG. 11) is pivotallysupported on housing 26 by a bracket 65. The bracket 65 includes a tubesection 66 and a configured end 67 with a juncture therebetweenconfigured to mateably engage the notch 43 in the side of housing 26.The configured end 67 includes a pair of flanges 68 with aperturesdefining an axis of rotation 69 for the pivot member 63. The pivotmember 63 is pivoted to the flanges 68 by a pivot pin and is rotatablearound the axis 69. By rotating the pivot member 63, the engagement ofteeth 60 and 64 and the related interfacing surfaces change in a mannercausing the actual pivot point along short leg 58 of L-shaped torquemember or bell crank 54 to change. (Compare FIGS. 9 and 9B.) As aresult, the distance from the end of spring 28 to the actual pivot pointchanges. This results in a shortening (or lengthening) in the torque armover which the spring 28 operates, which in turn results in asubstantial change in the force/displacement curve (compare the top andbottom curves in FIG. 9D). The change in moment arm is relatively easilyaccomplished because the spring 28 is not compressed substantiallyduring adjustment, since the interfacing surface on pivot member 63defines a constant radius around its axis of rotation. Thus, adjustmentis not adversely affected by the strength of spring 28. Nonetheless, theadjustment greatly affects the spring curve because of the resultingchange in the length of the moment arm over which the spring 28operates.

[0059] Pivoting of the pivot member 63 is accomplished through use of apair of apertured flanges 70 (FIG. 11) on the pivot member 63 that arespaced from axis 69. An adjustment rod 71 extends through tube section66 into configured end 67 and is pivoted to the apertured flanges 70.Rod 71 includes a threaded opposite end 72. An elongated nut 73 isthreaded onto rod end 72. Nut 73 includes a washer 73′ that rotatablyengages an end of the tube section 66, and further includes a configuredend 74 having longitudinally-extending ribs or slots shaped to mateablytelescopingly engage mating ribs 75 on a driving ring 76. A handle 77 isrotatably mounted on tube section 66 and is operably connected to thedriving ring 76 by an overtorque clutch ring 78. Clutch ring 78 includesresilient fingers 79 that operably engage a ring of friction teeth 80 onthe driving ring 76. Fingers 79 are shaped to frictionally slip overteeth 80 at a predetermined torsional load to prevent damage tocomponents of the chair 20. A retainer 81 includes resilient legs 81-that snappingly engage the end 74 of the nut 73 to retain the drivingring 76 and the clutch ring 78 together with a predetermined amount offorce. A spacer/washer 82 rides on the end of the nut 73 to provide abearing surface to better support the clutch ring 78 for rotation. Anend cap 83 visually covers an end of the assembly. The end cap 83includes a center protrusion 84 that snaps into the retainer 81 toforcibly keep the resilient legs of the retainer 81 engaged in the endof the nut 73.

[0060] In use, adjustment is accomplished by rotating the handle 77 ontube section 66, which causes nut 73 to rotate by means of clutch ring78 and driving ring 76 (unless the force required for rotation of thenut 73 is so great that the clutch ring 78 slips on driving ring 76 toprevent damage to the components). As the nut 73 rotates, the rod 71 isdrawn outwardly (or pressed inwardly) from the housing 26, causing thepivot member 63 to rotate. Pivoting the pivot member 63 changes thepoint of engagement (i.e. fulcrum point) of the pivot member 63 and theshort leg 58 of the L-shaped torque member or bell crank 54, thuschanging the moment arm over which the spring 28 acts.

Back-Stop Mechanism

[0061] The back-stop mechanism 36 (FIG. 8) includes a cam 86 pivoted tothe housing 26 at location 87. The cam 86 includes stop surfaces orsteps 88, detent depressions 89 that correspond to surfaces 88, andteeth 90. The steps 88 are shaped to mateably engage the seat-attachedbracket 56 to limit the rearward rotation of the back frame 30 bylimiting the rearward movement of the seat 24. This allows a seated userto limit the amount of recline to a desired maximum point. A leaf spring91 (FIG. 10) is attached to the housing 26 by use of a U-shaped finger92 that slips through a first hole and hooks into a second hole in thehousing 26. The opposite end of the leaf spring includes a U-shaped bend93 shaped to mateably slidably engage the detent depressions 89. Thedepressions 89 correspond to the steps 88 so that, when a particularstep 88 is selected, a corresponding depression 89 is engaged by spring91 to hold the cam 86 in the selected angular position. Notably, thesteps 88 (and the depressions 89) are located angularly close togetherin the area corresponding to chair positions close to the uprightposition of the back frame 30, and are located angularly farther apartin the area corresponding to more fully reclined chair positions. Thisis done so that seated users can select from a greater number ofback-stopping positions when near an upright position. It is noted thatseated users are likely to want multiple back-stopping positions thatare close together when near an upright position, and are less likely toselect a back-stopping position that is near the fully reclined chairposition.

[0062] The cam 86 is rotated through use of a control that includes apivoting lever 94, a link 95, and a rotatable handle 96. The pivotinglever 94 is pivoted generally at its middle to the housing 26 atlocation 97. One end of the pivoting lever 94 includes teeth 98 thatengage teeth 90 of cam 86. The other end of lever 94 is pivoted to rigidlink 95 at location 97′. Handle 96 includes a body 101 that is rotatablymounted on tube section 66 of MAS pivot bracket 65, and further includesa flipper 99 that provides easy grasping to a seated user. A protrusion100 extends from the body and is pivotally attached to link 95.

[0063] To adjust the back-stop mechanism 36, the handle 96 is rotated,which rotates cam 86 through operation of link 95 and lever 94. The cam86 is rotated to a desired angular position so that the selected step 87engages the seat-attached bracket 56 to prevent any further reclinebeyond the defined back-stop point. Since the seat 24 is attached to theback frame 30, this limits recline of the back 22.

[0064] A modified control for operating the back-stop cam 86 is shown inFIG. 11A. The modified control includes a pivoting lever 94A androtatable handle 96A connected to the handle 96A by a rotary pivot/slidejoint 380. The lever 94A includes teeth 381 that engage cam 86 and ispivoted to housing 26 at pivot 97, both of which are like lever 94.However, in the modified control, link 95 is eliminated and replacedwith the single joint 380. Joint 380 includes a ball 381 (FIG. 11B) thatextends from the lever 94A. A snap-on “car” or bearing 382 includes asocket 383 for pivotally engaging ball 381 to define a ball-and-socketjoint. The bearing 382 includes outer surfaces 384 that slidably engagea slot 385 in a radially-extending arm 386 on handle 96A (Fig. 11C). Thejoint 380 operably connects the handle 96A to the lever 94A, despite thecomplex movement resulting from rotation of the handle 96A about a firstaxis, and from rotation of the lever 94A about a second axis that isskewed relative to the first axis. Advantageously, the modified controlprovides an operable interconnection with few parts, and with parts thatare partially inside of the control housing 26, such that the parts aresubstantially hidden from view to a person standing beside the chair.

Back Construction

[0065] The back frame 30 and back shell 31 (FIG. 12) form a compliantback support for a seated user that is particularly comfortable andsympathetic to back movements of the seated user, particularly in thelumbar area of the back 22. Adjustment features on the assembly providefurther comfort and allow a seated user to customize the chair to meethis/her particular needs and preferences in the upright through reclinedpositions.

[0066] The back frame 30 (FIG. 12A) is curvilinearly shaped and forms anarch across the back area of the chair 20. A variety of constructionsare contemplated for back frame 30, and accordingly, the presentinvention should not be improperly limited to only a particular one. Forexample, the back frame 30 could be entirely metal, plastic, or acombination thereof. Also, the rigid internal reinforcement 102described below could be tubular, angle iron, or a stamping. Theillustrated back frame 30 includes a looping or arch-shaped internalmetal reinforcement 102 and an outer molded-on polymeric skin orcovering 103. (For illustrative purposes, the covering 103 is shown asif it is transparent (FIG. 12A), so that the reinforcement 102 is easilyseen.) The metal reinforcement 102 includes a looping intermediate rodsection 104 (only half of which is shown in FIG. 12A) having a circularcross-section. Reinforcement 102 further includes configuredends/brackets 105 welded onto the ends of the intermediate section 104.One or two of T-shaped top pivot connectors 107 are attached tointermediate section 104 near a top portion thereof. Notably, a singletop connector 107, when used, allows greater side-to-side flexibilitythan with two top connectors, which may be desired in a chair where theuser is expected to often twist his/her torso and lean to a side in thechair. A pair of spaced-apart top connectors 107 provide a stifferarrangement. Each connector 107 (FIG. 12B) includes a stem 108 welded tointermediate section 104 and includes a transverse rod section 109extended through stem 108. The rod section 109 is located outboard ofthe skin or shell 103 and is adapted to snap-in frictionally andpivotally engage a mating recess in the back shell 31 for rotation abouta horizontal axis, as described below. The present invention iscontemplated to include different back frame shapes. For example, theinverted U-shaped intermediate section 104 of back frame 30 can bereplaced with an inverted T-shaped intermediate section having a lowertransverse member that is generally proximate and parallel the beltbracket 132, and a vertical member that extends upwardly therefrom. In apreferred form, each back frame of the present chair definesspaced-apart lower connections or apertures 113 that define pivot pointsand a top connection(s) 107 forming a triangular tripod-likearrangement. This arrangement combines with the semi-rigidresiliently-flexible back shell 31 to posturally flexibly support andpermit torsional flexing of a seated user's torso when in the chair. Inan alternative form, the lower connections 113 could occur on the seatinstead of the back of the chair.

[0067] The configured ends 105 include an inner surface 10′ (FIG. 13)that may or may not be covered by the outer shell 103. In theillustrated back frame 30 of FIGS. 12A and 4A, the reinforcement 102 issubstantially covered by the shell 103, but a pocket is formed on aninside surface at configured ends 105 at apertures 111-113. Theconfigured ends 105 include extruded flanges forming apertures 111-113which in turn define the back-tilt axis 23, the seat-tilt axis 25, and abottom pivotal connection for the back shell 31, respectively. Theapertures 111 and 112 (FIG. 13) include frustoconically-shaped flanges116 defining pockets for receiving multi-piece bearings 114 and 115,respectively. Bearing 114 includes an outer rubber bushing 117 engagingthe flanges 116 and an inner lubricous bearing element 118. A pivot stud119 includes a second lubricous bearing element 120 that matinglyslidingly engages the first bearing element 118. The stud 119 isextended through bearing 114 in an outward direction and threadably intowelded nut 51 on side arms 49 of the base frames 26, 45, and 49. Thebearing element 118 bottoms out on the nut 51 to prevent over-tighteningof the stud 119. The head of the stud 119 is shaped to slide through theaperture 111 to facilitate assembly by allowing the stud to be threadedinto nut 51 from the inboard side of the side arm 49. It is noted thatthe head of stud 119 can be enlarged to positively capture theconfigured end 105 to the side arm 49 if desired. The presentarrangement including the rubber bushings 117 allows the pivot 23 toflex and compensate for rotation that is not perfectly aligned with theaxis 23, thus reducing the stress on the bearings and reducing thestress on components of the chair such as on the back frame 30 and theside arms 49 where the stud 119 is misaligned with its axis.

[0068] The lower seat-to-back frame bearing 115 is similar to bearing114 in that bearing 115 includes a rubber bushing 121 and a lubricousbearing element 122, although it is noted that the frustoconical surfacefaces inwardly. A welded stud 123 extends from seat carrier 124 andincludes a lubricous bearing element 125 for rotatably and slidablyengaging the bearing element 122. It is noted that in the illustratedarrangement, the configured end 105 is trapped between the side arms 49of base frames 26, 45, and 49 and the seat carrier 124, such that thebearings 114 and 115 do not need to be positively retained to theconfigured ends 105. Nonetheless, a positive bearing arrangement couldbe readily constructed on the pivot 112 by enlarging the head of thestud 119 and by using a similar headed stud in place of the welded stud123.

[0069] A second configuration of the configured end of back frame 30 isshown in FIG. 13A. Similar components are identified by identicalnumbers, and modified components are identified with the same numbersand with the addition of the letter “A.” In the modified configured end105A, the frustoconical surfaces of pivots 111A and 112A face inopposite directions from pivots 111 and 112. Pivot 112A (including awelded-in stud 123A that pivotally supports the seat carrier 124 on theback frame 30) includes a threaded axial hole in its outer end. Aretainer screw 300 is extended into the threaded hole to positivelyretain the pivot assembly together. Specifically, a washer 301 on screw300 engages and positively retains the bearing sleeve 125 that mountsthe inner bearing element 122 on the pivot stud 123A. The taper in thepocket and on the bearing outer sleeve 121 positively holds the bearing115A together. The upper pivot 111A that pivotally supports the backframe 30 on the side arms 50 of the base frame is generally identical tothe lower pivot 112, except that the pivot 111A faces in an oppositeinboard direction. Specifically, in upper pivot 111A, a stud 119A iswelded onto side arm 50. The bearing is operably mounted on the stud119A in the bearing pocket defined in the base frame 30 and held inplace with another washered screw 300. For assembly, the back frame 30is flexed apart to engage bearing 115, and the configured ends 105A aretwisted and resiliently flexed, and thereafter are released such thatthey spring back to an at-rest position. This arrangement provides aquick assembly procedure that is fastenerless, secure, and readilyaccomplished.

[0070] The present back shell system shown in FIGS. 12, 15, and 16 (andthe back systems of FIGS. 12D-121) is compliant and designed to worksympathetically with the human back. The word “compliant” as used hereinis intended to refer to the flexibility of the present back especiallyin the lumbar area (see FIGS. 12 and 12F-12I) or a back structure thatprovides the equivalent of that flexibility (see FIGS. 12D and 12E), andthe word “sympathetically” is intended to mean that the back moves inclose harmony with a seated user's back as the chair back 22 is reclinedand when a seated user flexes his/her lower back and posturally supportsthe seated user's back. The back shell 31 has three specific regions, asdoes the human back, those being the thoracic region, the lumbar region,and the pelvic region.

[0071] The thoracic “rib cage” region of a human's back is relativelystiff. For this reason, a relatively stiff upper shell portion (FIG. 12)is provided that supports the relatively stiff thoracic (rib cage)region 252 of a seated user. It carries the weight of a user's torso.The upper pivot axis is strategically located directly behind theaverage user's upper body center of gravity, balancing his/her backweight for good pressure distribution.

[0072] The lumbar region 251 of a human's back is more flexible. Forthis reason, the shell lumbar region of back shell 31 includes twocurved, vertical-living hinges 126 at its side edges (FIG. 15) connectedby a number of horizontal “cross straps” 125′ . These straps 125′ areseparated by widthwise slots 125′ allowing the straps to moveindependently. The slots 125′ may have radiused ends or teardrop-shapedends to reduce concentration of stress. This shell area is configured tocomfortably and posturally support the human lumbar region. Both sidestraps 125′ are flexible and able to substantially change radius ofcurvature from side to side. This shell region automatically changescurvature as a user changes posture, yet maintains a relativelyconsistent level of support. This allows a user to consciously (orsubconsciously) flex his/her back during work, temporarily moving stressoff of tiring muscles or spinal disc portions onto different ones. Thisfrequent motion also “pumps” nutrients through the spine, keeping itnourished and more healthy. When a specific user leans against the shell31, he/she exerts unique relative pressures on the various lumbar “crossstraps.” This causes the living hinges to flex in a unique way, urgingthe shell to conform with a user's unique back shape. This provides moreuniform support over a larger area of the back improving comfort anddiminishing “high pressure points.” The cross straps can also flex tobetter match a user's side-to-side shape. The neutral axis of the humanspine is located well inside the back. Correspondingly, the “sidestraps” are located forward of the central portion of the lumbar region(closer to the spine neutral axis), helping the shell flexure mimichuman back flexure.

[0073] The pelvic region 250 is rather inflexible on human beings.Accordingly, the lowest portion of the shell 31 is also ratherinflexible so that it posturally/mateably supports the inflexible humanpelvis. When a user flexes his/her spine rearward, the user's pelvisautomatically pivots about his/her hip joint and the skin on his/herback stretches. The lower shell/back frame pivot point is strategicallylocated near but a bit rearward of the human hip joint. Its nearnessallows the shell pelvic region to rotate sympathetically with a user'spelvis. By being a bit rearward, however, the lumbar region of the shellstretches (the slots widen) somewhat less than the user's back skin,enough for good sympathetic flexure, but not so much as to stretch orbunch up clothing.

[0074] Specifically, the present back shell construction 31 (FIG. 4A)comprises a resiliently-flexible molded sheet made from polymericmaterial such as polypropylene, with top and bottom cushions positionedthereon (see FIG. 4A). The back shell 31 (FIG. 16) includes a pluralityof horizontal slots 125_in its lower half that are located generally inthe lumbar area of the chair 20. The slots 125_extend substantiallyacross the back shell 31, but terminate at locations spaced from thesides so that resilient vertical bands of material 126 are formed alongeach edge. The bands of material or side straps 126 are designed to forma naturally forwardly-convex shape, but are flexible so that theyprovide an optimal lumbar support and shape to a seated user. The bands126 allow the back shell to change shape to conform to a user's backshape in a sympathetic manner, side to side and vertically. A ridge 127extends along the perimeter of the shell 31. A pair of spaced-apartrecesses 128 are formed generally in an upper thoracic area of the backshell 31 on its rearward surface. The recesses 128 (FIGS. 14A and 14B)each include a T-shaped entrance with the narrow portion 129 of therecesses 128 having a width for receiving the stem 108 of the topconnector 32 on the back frame 30 and with the wider portion 130 of therecesses 128 having a width shaped to receive the transverse rod section109 of the top connector 32. The recesses 128 each extend upwardly intothe back shell 31 such that opposing flanges 131 formed adjacent thenarrow portion 129 pivotally capture the rod section 109 of the T-topconnector 107 as the stem 108 slides into the narrow portion 129. Ridges132 in the recesses 128 frictionally positively retain the topconnectors 107 and secure the back shell 31 to the back frame 30, yetallow the back shell 31 to pivot about a horizontal axis. This allowsfor the back shell 31 to flex for optimal lumbar support withoutundesired restriction.

[0075] A belt bracket 132 (FIG. 16) includes an elongated center stripor strap 133 that matches the shape of the bottom edge of the back shell31 and that is molded into a bottom edge of the back shell 31. The strip133 can also be an integral part of the back shell or can be attached toback shell 31 with screws, fasteners, adhesive, frictional tabs,insert-molding techniques, or in other ways of attaching known in theart. The strip 133 includes side arms/flanges 134 that extend forwardlyfrom the ends of strip 133 and include apertures 135. The torsionaladjustment lumbar mechanism 34 engages the flanges 134 and pivotallyattaches the back shell 31 to the back frame at location 113 (FIG. 4A).The torsional adjustment lumbar spring mechanism 34 is adjustable andbiases the back shell 31 to a forwardly-convex shape to provide optimallumbar support for a seated user. The torsional adjustment lumbar springmechanism 34 cooperates with the resilient flexibility of the back shell31 and with the shape-changing ability of the vertically-adjustablelumbar support 35 to provide a highly-adjustable and comfortable backsupport for a seated user.

[0076] The pivot location 113 is optimally chosen to be at a rear of thehip bone and somewhat above the seat 24. (See FIG. 12.) Optimally, thefore/aft distance from pivot location 113 to strip 133 is approximatelyequal to the distance from a seated user's hip joint/axis to his/herlower spine/tail bone region so that the lower back 250 moves similarlyand sympathetically to the way a seated user's lower back moves duringflexure about the seated user's hip joint. The location 113 incombination with a length of the forwardly-extending side flanges 133causes back shell 31 to flex in the following sympathetic manner. Thepelvic supporting area 250 of the back shell construction 31 movessympathetically rearwardly and downwardly along a path selected to matcha person's spine and body movement as a seated user flexes his/her backand presses his/her lower back against the back shell construction 31.The lumbar support area 251 simultaneously flexes from aforwardly-concave shape toward a more planar shape. The thoracic supportarea 252 rotates about top connector 107 but does not flex a substantialamount. The total angular rotation of the pelvic and thoracic supportingareas 250 and 252 are much greater than in prior art synchrotilt chairs,which provides substantially increased comfort. Notably, the back shellconstruction 31 also flexes in a horizontal plane to provide goodpostural support for a seated user who twists his/her torso to reach anobject. Notably, the back frame 30 is oriented at about a 5° rearwardangle from vertical when in the upright position, and rotates to about a30° rearward angle from vertical when in the fully reclined position.Concurrently, the seat-tilt axis 25 is rearward and at an angle of about60° below horizontal from the back-tilt axis 23 when the back frame 30is in the upright position, and pivots to almost vertically below theback-tilt axis 23 when the back frame 30 is in the fully reclinedposition.

[0077] Back constructions 31A-31F (FIGS. 12D-12I, respectively) areadditional constructions adapted to provide a sympathetic back supportsimilar in many aspects to the back shell construction 31. Like backconstruction 31, the present invention is contemplated to includeattaching the back constructions 31A-31F to the seat or the base frameat bottom connections. Specifically, the illustrated constructions31A-31F are used in combination with back frame 30 to provide a specificsupport tailored to thoracic, lumbar, and pelvic regions of a seateduser. Each of the back constructions 31A-31F are pivoted at top andbottom pivot connections 107 and 113, and each include side arms 134 forflexing about a particularly located lever pivot axis 113. However, theback constructions 31A-31F achieve their sympathetic back support inslightly different ways.

[0078] Back construction 31A (FIG. 12D) includes a cushioned top backsupport 255 pivoted at top pivot connection 107, and further includes acushioned bottom back support 256 pivoted at bottom location 113 by thebelt bracket 132 including side flanges 134. Top and bottom backsupports 255 and 256 are joined by a pivot/slide connection 257.Pivot/slide connection 257 comprises a bottom pocket formed by a pair offlanges 258, and top flange 259 that both slides and pivots in thepocket. A torsional lumbar support spring mechanism 34 is attached atbottom pivot location 113 and, if desired, also at connection 107 tobias top and bottom back supports 255 and 256 forwardly. The combinationprovides a sympathetic back support that moves with a selected user'sback to match virtually any user's back shape, similar to the back shellconstruction 31 described above.

[0079] Back construction 31B (FIG. 12E) includes a top back support 261pivoted at top connection 107, a bottom back support 262 pivoted atlower connection 113 on belt bracket side flange 134, and anintermediate back support 262 operably positioned therebetween.Intermediate back support 262 is pivoted to bottom back support 262 atpivot 263, and is slidably pivoted to top back support 261 atpivot/slide joint 264. Pivot/slide joint 264 is formed by top flanges265 defining a pocket, and another flange 266 with an end that pivotsand slides in the pocket. Springs are positioned at one or more joints107, 113, and 264 to bias the back construction 260 to aforwardly-concave shape.

[0080] Back construction 31C (FIG. 12F) is similar to back shellconstruction 31 in that it includes a sheet-like flexible shell withtransverse lumbar slits. The shell is pivoted at top and bottomconnections 107 and 113 to back frame 30. The shell of back construction31C is biased toward a forwardly-convex shape by a torsional lumbarsupport spring mechanism 34 at bottom pivot 113 and at top pivot 107, bya curvilinear leaf spring 271 in the lumbar area of the shell, by aspring 272 that presses the shell forwardly off of an intermediatesection of back frame 30, and/or by a vertical spring 273 that extendsfrom top connection 107 to a rear pivot on belt bracket side flange 134.

[0081] Back construction 31D (FIG. 12G) includes a transverse leafspring 276 that spans between the opposing sides of back frame 30, andthat biases the lumbar area of its back shell 277 forwardly, much likespring 272 in the back construction 270. Back construction 31E (FIG.12H) includes vertical leaf springs 279 embedded in its back shell 280that bias the lumbar area of back shell 280 forwardly, much like springs271 in back construction 270. Notably, back construction 278 includesonly a single top pivot connection 107. Back construction 31F (FIG. 12I)includes a vertical spring 282 connected to a top of the back frame 30,and to belt bracket 132 at a bottom of its back shell 283. Since theback shell 283 is forwardly convex, the spring 282 biases the shell 283toward an even more convex shape, thus providing additional lumbarsupport. (Compare to spring 273 on back construction 31C, FIG. 12F.)

[0082] It is contemplated that the torsional lumbar support springmechanism 34 (FIG. 12I) can be designed in many different constructions,but includes at least a spring operably connected between the back frame30 and the back shell 31. Optionally, the arrangement includes a tensionadjustment device having a handle and a friction latch to provide fortension adjustment. The spring biases the belt bracket 132 rotationallyforward so that the back shell 31 defines a forwardly-convex shapeoptimally suited for lumbar support to a seated user. By rotating thehandle to different latched positions, the tension of the spring isadjusted to provide an optimal forward lumbar force. As a seated userpresses against the lumbar area of back shell 31, the back shell 31flexes “sympathetically” with a movement that mirrors a user's spine andbody flesh. The force of the bands of material 126 in the shell 31provide a relatively constant force toward their natural curvilinearshape, but when combined with the torsional lumbar support springmechanism 34, they provide a highly-adjustable bias force for lumbarsupport as the user leans against the lumbar area. It is noted that afixed non-adjustable spring biasing the back belt of the back shell flexzone directly could be used, or that an adjustable spring onlyadjustable during installation could be used. However, the presentadjustable device allows the greatest adjustment to meet varying needsof seated users. Thus, a user can assume a variety of well-supportedback postures.

[0083] In the present torsional lumbar support spring mechanism 34 (FIG.12I), belt bracket 132 is pivoted to back frame 30 by a stud 290 thatextends inboard from back frame 30 through a hole 291 in belt bracketside flange 134. A bushing 292 engages the stud 290 to provide forsmooth rotation, and a retainer 293 holds the stud 290 in hole 291. Abase 294 is screwed by screws 294_ or welded to back frame 30, andincludes a protrusion 295 having a sun gear 296 and a protruding tip 297on one end. A hub 298 includes a plate 299 with a sleeve-like boss 300for receiving the protrusion 295. The boss 300 has a slot 301 forreceiving an inner end 302 of a spiral spring 303. The body of spring303 wraps around protrusion 295, and terminates in a hooked outer end304. Hub 298 has a pair of axle studs 305 that extend from plate 299 ina direction opposite boss 300. A pair of pie-shaped planet gears 306 arepivoted to axle studs 305 at pivot holes 307. A plurality of teeth 308are located in an arch about pivot holes 307 on the planet gears 306,and a driver pin 309 is located at one end of the arc. A cup-shapedhandle 310 is shaped to cover gears 306, hub 298, spring 303, and base294. The handle 310 includes a flat end panel 311 having a centered hole312 for rotatably engaging the protruding tip 297 of base 294. A pair ofopposing spirally-shaped recesses or channels 313 are formed in the endpanel 311. The recesses 313 include an inner end 314, an outer end 315,and an elongated portion having a plurality of detents or scallops 316formed between the ends 314 and 315. The recesses 313 mateably receivethe driver pins 309. The hooked outer end 304 engages fingers 317 onbelt bracket 132, which fingers 317 extend through an arcuate slot 318in the configured end 105 of back frame 30.

[0084] Handle 310 is rotated to operate torsional lumbar support springmechanism 34. This causes recesses 313 to engage driver pins 309 onplanet gears 306. The planet gears 306 are geared to sun gear 296, suchthat planet gears 306 rotate about sun gear 296 as the driver pins 309are forced inwardly (or outwardly) and the planet gears 306 are forcedto rotate on their respective pivots/axles 305. In turn, as planet gears306 rotate, they force hub 298 to rotate. Due to the connection ofspiral spring 303 to hub 298, spiral spring 303 is wound tighter (orunwound). Thus, the tension of spring 303 on belt bracket 132 isadjustably changed. The detents 316 engage the driver pins 309 withenough frictional resistance to hold the spring 303 in a desiredtensioned condition. Due to the arrangement, the angular winding ofspiral spring 303 is greater than the angular rotation of handle 310.

[0085] In a modified torsional lumbar support spring mechanism 34A (FIG.12K), a base bracket 244A is attached to configured end 105A of backframe 30. A lever 306A and driver 298A are operably mounted on basebracket 244A to wind a spiral spring 303A as a handle 310A is rotated.Specifically, the base bracket 244A includes a pivot pin 290 thatpivotally engages hole 291 in belt bracket 132. A second pin 317 extendsthrough arcuate slot 318 in configured end 105A, which slot 318 extendsaround pivot pin 290 at a constant radius. Two pins 360 and 361 extendfrom base bracket 244A opposite pivot pin 290. The driver 298A includesan apertured end 362 with a hole 363 for rotatably engaging center pin360. The end 362 includes an outer surface 364 with a slot therein forengaging an inner end 365 of spiral spring 303A. The outer end 365 ishook-shaped to securely engage pin 317 on the belt bracket 132. Afinger-like stud 366 extends laterally from the outer end 367 of driver298A.

[0086] Lever 306A includes a body with a hole 368 for pivotally engagingpin 361, and a slot 369 extending arcuately around hole 368. A pin 370extends from lever 306A for engaging a spiral cam slot 313A on an insidesurface of cup-shaped handle 310A. A tooth 371 on lever 306A ispositioned to engage stud 366 on driver 298A. Hole 372 on handle 310Arotatably engages the pivot pin 360 on base bracket 244A.

[0087] Handle 310A is rotatable between a low tension position (FIGS.12L and 12LL) and a high tension position (FIGS. 12M and 12MM).Specifically, as handle 310A is rotated, pin 370 rides along slot 313Acausing lever 306A to rotate about hole 368 and pivot pin 361. As lever306A rotates, tooth 371 engages pin 366 to rotate driver 298A about pin360. Rotation of driver 298A causes the inside end 365 of spring 303A torotate, thus winding (or unwinding) spring 303A. The arrangement ofdriver 298A, lever 360A, and handle 310A provide a mechanical advantageof about 4:1, so that the spiral spring 303A is adjustably wound with adesired amount of adjustment force on the handle 310A. In theillustration, a rotation of about 330° of the handle 310A produces aspring tension adjustment winding of about 80.°

[0088] Optionally, for maximum adjustability, a vertical adjustablelumbar system 35 (FIG. 16) is provided that includes a slide frame 150(FIG. 19) that is generally flat and that includes several hooked tabs151 on its front surface. A concave lumbar support sheet 152 (FIG. 16)of flexible material such as spring steel includes a plurality ofvertical slots that form resilient leaf-spring-like fingers 153 alongthe top and bottom edges of the sheet 152. The (optional) heightadjustable back support sheet 152 is basically a radiused sheet springthat can, with normal back support pressures, deflect until it matchesthe shape of the back shell beneath it. In doing so, it provides a bandof higher force across the back. This provides a user withheight-adjustable localized back support, regardless of the flexuralshape of the user's back. Thus, it provides the benefits of atraditional lumbar height adjustment without forcing a user into aparticular rigid back posture. Further, the fabric or upholstery on theback is always held taunt, such that wrinkles are eliminated. Stretchfabric can also be used to eliminate wrinkles.

[0089] A user may also use this device for a second reason, that reasonbeing to more completely adapt the back shell shape to his/her ownunique back shape. Especially in the lower lumbar/pelvic region, humansvary dramatically in back shape. Users with more extreme shapes willbenefit by sliding the device into regions where their back does notsolidly contact the shell. The device will effectively change its shapeto exactly “fill in the gap” and provide good support in this area. Noother known lumbar height adjuster does this in the manner describedbelow.

[0090] Four tips 154 on fingers 153 form retention tabs that areparticularly adapted to securely engage the hooked tabs 151 to retainthe sheet 152 to the slide frame 150. The remaining tips 155 of thefingers 153 slidably engage the slide frame 150 and hold the centralportion 156 of the concave sheet forwardly and away from the slide frame150. The slide frame 150 is vertically adjustable on the back shell 31(FIG. 16) and is positioned on the back shell 31 between the back shell31 and the back cushion. Alternatively, it is contemplated that theslide frame 150 could be located between the back cushion and under theupholstery covering the back 22, or even on a front face of the back 22outside the upholstery sheet covering the back 22. By adjusting theslide vertically, this arrangement allows a seated user to adjust theshape of the lumbar area on the back shell 31, thus providing a highdegree of comfort. A laterally-extending guide 157 (FIG. 19) is formedat each of the ends of the slide frame 150. The guides 157 includeopposing flanges 158 forming inwardly-facing grooves. Molded handles 159(FIG. 20) each include a leg 160 shaped to mateably telescopingly engagethe guides 157 (FIGS. 17 and 18). The handles 159 further include aC-shaped lip 160 shaped to snappingly engage and slide along the edgeridge 127 along the edge of back shell 31. It is contemplated that othermeans can be provided for guiding the vertical movement of the slideframe 150 on back shell 31, such as a cord, a track molded along butinward of the edge of the back shell, and the like. An enlarged flat endportion 161 of handle 159 extends laterally outwardly from molded handle159. Notably, the end portion 161 is relatively thin at a location 161immediately outboard of the lip 160, so that the handle 159 can beextended through a relatively thin slot along the side edge of the back22 when a cushion and upholstery sheet are attached to the back shell31.

[0091] The illustrated back 22 of FIG. 12 includes a novel constructionincorporating stretch fabric 400 sewn at location 401 to a lower edge ofthe upholstery sheet 402 for covering a front of the back 22. Thestretch fabric 400 is further sewn into a notch 406 in an extrusion 403of structural plastic, such as polypropylene or polyethylene. Theextrusion 403 is attached to a lower portion 404 of the back shell 31 bysecure means, such as snap-in attachment, hook-in attachment, rivets,screws, other mechanical fasteners, or other means for secureattachment. The foam cushion 405 of the back 22 and thevertically-adjustable lumbar support device 35 are positioned betweenthe sheet 402 and back shell 31. It is contemplated that the stretchfabric will have a stretch rate of at least about 100%, with a recoveryof at least 90% upon release. The stretch fabric 400 and sheet 402 aresewn onto the back 22 in a tensioned condition, so that the sheet 402does not wrinkle or pucker despite the large flexure of the lumbarregion 251 toward a planar condition. The stretch fabric 400 is in a lowvisibility position, but can be colored to the color of the chair ifdesired. It is noted that covering 402 can be extended to cover the rearof back 22 as well as its front.

Primary Seat Movement. Seat Undercarriage/Support Frame and BearingArrangement

[0092] The seat 24 (FIG. 4B) is supported by an undercarriage thatincludes a seat front slide 162 and the seat carrier 124. Where seatdepth adjustment is desired, a manually depth-adjustable seat frame 163is slidably positioned on the seat carrier 124 (as is shown in FIGS. 4Band 21-30). Where seat depth adjustment is not desired, the features ofthe seat frame 163 and seat rear carrier 124 can be incorporated into asingle component, such as is illustrated in FIG. 29 by frame member163′. A seat shell 164 (FIG. 4B) includes a buttock-supporting rearsection 165 that is positioned on the seat carrier 124. Thebuttock-supporting rear section 165 carries most of the weight of theseated user, and acts somewhat like a perch in this regard. The seatshell 164 further includes a thigh-supporting front section 166 thatextends forwardly of the seat frame 163. Front section 166 is connectedto rear section 165 by a resilient section 167 strategically locatedgenerally under and slightly forward of a seated user's hip joint. Theresilient section 167 has a plurality of transverse slots 168 therein.The slots 168 are relatively short and are staggered across the seatshell 164, but are spaced from the edges of the seat shell 164, suchthat the band of material 169 at the edges of the seat shell 164 remainsintact and uninterrupted. The bands 169 securely connect the front andrear sections 166 and 165 together and bias them generally toward aplanar condition. A seat cushion 170 is positioned on seat frame 163 andis held in place by upholstery sheet and/or adhesive or the like.

[0093] Slide 162 (FIG. 4B) includes a top panel 171 with C-shaped sideflanges 172 that extend downwardly and inwardly. A linear lubricous cap173 is attached atop each sidewall of housing 26 and a mating bearing174 is attached inside of C-shaped side flanges 172 for slidablyengaging the lubricous cap 173. In this way, the slide 162 is capturedon the housing 26 for fore-to-aft sliding movement. The seat-attachedbracket 56 is attached under the top panel 171 and is located to operatewith the back-stop mechanism 36. An axle 174′ is attached atop the toppanel 171 and includes ends 175 that extend laterally from the slide162.

[0094] Seat carrier 124 (FIG. 4B) is T-shaped in plan view. Seat carrier124 is stamped from sheet metal into a “T” shape, and includes arelatively wide rear section 176 and a narrower front section 177.Embossments such as elongated embossments 178, 179, and 180 are formedin sections 176 and 177 along with side-down flanges 181 and side-upflanges 182 to stiffen the component. Two spaced-apart stop tabs 183 anda series of latch apertures 184 are formed in the front section 177 forreasons discussed below. The welded studs 123 are attached to side-upflanges 182 and extend laterally. As discussed above, the studs 123define the seat-tilt axis 25 at this location.

[0095] Seat frame 163 (FIG. 4B) is T-shaped, much like the seat carrier124, but seat frame 163 is shaped more like a pan and is generallylarger than the seat carrier 124 so that it is better adapted to supportthe seat shell 164 and seat cushion 170. Seat frame 163 includes a frontportion 185 and a rear portion 186. The front portion 185 includes a toppanel 187 with down flanges 188 at its sides. Holes 189 at the front ofdown flanges 188 form a pivot axis for the active thigh flex device 190described below. Other holes 191 spaced rearwardly of the holes 189support an axle that extends laterally and supports a multi-functionalcontrol 192 for controlling the seat depth adjustment and forcontrolling the active thigh flex device 190. The center of frontportion 185 is raised and defines a sidewall 193 (FIG. 23) having threeapertures 194-196 that cooperate to pivotally and operably support adepth latch 197. A depression 198 is formed in the center of frontportion 185 and a slot 200 is cutout in the center of the depression198. A T-shaped stop limiter 199 (FIG. 26) is positioned in thedepression 198 and screw-attached therein, with the stem 201 of thelimiter 199 extending downwardly through the slot 200 (FIGS. 26 and26A). An inverted U-shaped bracket 203 is attached to the wide rearsection 176. The U-bracket 203 (FIG. 28) includes apertures forpivotally supporting one end of a gas spring 204 used in the activethigh flex support device 190 described below. The rear section 176(FIG. 23) includes a U-shaped channel section 205 that extends aroundits perimeter and an outermost perimeter flange 206, both of which serveto stiffen the rear section 176. Flat areas 205_are formed on opposingsides of the rear section 176 for slidably engaging the top of rearbearings 209.

Seat Depth Adjustment

[0096] A pair of parallel elongated brackets 207 (FIG. 4B) are attachedunder the forwardly-extending outer sides of the U-shaped channelsection 205 for slidingly supporting the seat frame 163 on the seatcarrier 124. The elongated Z-brackets 207 form inwardly-facing C-shapedguides or tracks (FIG. 21) that extend fore-to-aft under the seat frame163. A bearing member is attached inside the guides of bracket 207 toprovide for smooth operation if desired. Two spaced-apart front bearings208 (FIG. 4B) and two spaced-apart rear bearings 209 are attached atopthe seat carrier 124, front bearings 208 being attached to front section177, and rear bearings 209 being attached to rear section 176. The rearbearings 209 are configured to slidably engage the guides in brackets207, and further include a tongue 210 that extends inwardly into theC-shaped portion of the C-shaped guides. The tongue 210 captures theseat frame 163 so that the seat frame 163 cannot be pulled upwardly awayfrom the seat carrier 124. The front bearings 208 slidably engage theunderside of the front section 187 at spaced-apart locations. The frontbearings 208 can also be made to capture the front portion of the seatframe 163; however, this is not deemed necessary due to the thigh flexdevice, which provides this function.

[0097] The depth adjustment of seat 24 is provided by manually slidingseat frame 163 on bearings 208 and 209 on seat carrier 124 between arearward position for minimum seat depth (see FIG. 24) and a forwardposition for maximum seat depth (see FIG. 25). The stem 201 (FIG. 26A)of limiter 199 engages the stop tabs 183 in seat carrier 124 to preventthe seat 24 from being adjusted too far forwardly or too far rearwardly.The depth latch 197 (FIG. 23) is T-shaped and includes pivot tabs 212and 212′ on one of its arms that pivotally engages apertures 194 and 195in seat frame 163. The depth latch 197 further includes adownwardly-extending latching tooth 213 on its other arm that extendsthrough aperture 195 in seat frame 163 into a selected one of the seriesof slots 214 (FIG. 26) in the seat carrier 124. A “stem” of the depthlatch 197 (FIG. 23) extends laterally outboard and includes an actuationtab 215. Multi-function control 192 includes an inner axle 217 thatsupports the main components of the multi-function control. One of thesecomponents is an inner sleeve 218 rotatably mounted on axle 217. Thehandle 219 is connected to an outer end of the inner sleeve 218 and aprotrusion 220 is connected to an inner end of the inner sleeve 218. Theprotrusion 220 is connected to the actuation tab 215, such that rotationof the handle 219 moves the protrusion 220 and pivots the latch 197about latch pivots 194 and 195 in an up and down disconnection. Theresult is that the latching tooth 213 is released from the series ofslots 214, so that the seat 24 can be adjusted to a new desired depth. Aspring on inner sleeve 218 biases the latch 197 to a normally engagedposition. It is contemplated that a variety of different springarrangements can be used, such as by including an internal springoperably connected to inner sleeve 218 or to latch 197.

Seat Active Thigh Angle Adjustment (with Infinitely Adjustable GasSpring)

[0098] A front reinforcement plate 222 (FIG. 28) is attached to theunderside of the thigh-supporting front section 166 of seat shell 164. AZ-shaped bracket 221 is attached to plate 222 and a bushing 223 issecured between the bracket 221 and the plate 222. A bent rod axle 224is rotatably supported in bushing 223 and includes end sections 225 and226 that extend through and are pivotally supported in apertures 190 ofdown flanges 189 of seat frame 163. The end section 226 includes a flatside, and a U-shaped bracket 227 is non-rotatably attached to the endsection 226 for supporting an end of gas spring 204. The U-shapedbracket 227 is oriented at an angle to a portion of the bent rod axle224 that extends toward bushing 223, such that the U-shaped bracket 227acts as a crank to raise and lower the thigh-supporting front portion166 of seat shell 164 when the gas spring 204 is extended or retracted.Specifically, the gas spring 204 is operably mounted between brackets227 and 203, so that when extended, the front thigh-supporting section166 of seat shell 164 is moved upwardly to provide additional thighsupport. Notably, the thigh-supporting section 166 provides some flexeven when the gas spring 204 is locked in a fixed extension, so that aperson's thighs are comfortably supported at all times. Nonetheless, theinfinite adjustability of this active thigh support system provides animproved adjustability that is useful, particularly to people withshorter legs.

[0099] The gas spring 204 (FIG. 28) is self-locking and includes arelease button 233 at its rear end that is attached to the bracket 203for releasing the gas spring 204 so that its extendable rod isextendable or retractable. Such gas springs 204 are well-known in theart. The multi-functional control 192 (FIG. 3) includes an actuator foroperating the release button 233. Specifically, the multi-functionalcontrol 192 includes a rotatably outer sleeve 229 (FIG. 23) operablypositioned on the inner sleeve 218 and a handle 230 for rotating theouter sleeve 229. A connector 231 extends radially from an inboard endof outer sleeve 229. A cable 232 extends from the connector 231 on outersleeve 229 to the release button 233 (FIG. 28). The cable 232 has alength chosen so that when outer sleeve 229 is rotated, the cable 232pulls on the release button 233 causing the internal lock of the gasspring 204 to release. The release button 233 is spring biased to anormally locked position. A seated user adjusts the active thigh flexsupport system by operating the handle 230 to release the gas spring204. The seated user then presses on (or raises his/her legs away from)the thigh-supporting front portion 166 of the seat shell 164 causing thegas spring 230 to operate the bent rod axle 217 to re-adjust thethigh-supporting front portion 166. Notably, the active thigh supportsystem 190 provides for infinite adjustment within a given range ofadjustment.

[0100] Also shown on the control 192 (FIG. 10) is a second rotatablehandle 234 operably connected to a pneumatic vertical height adjustmentmechanism for adjusting chair height by a Bowden cable 235, sleeve 235′,and side bracket 235′. The details of chair height adjustment mechanismsare well known, such that they do not need to be discussed herein.

[0101] The seat shell 164 and its supporting structure (FIG. 4B) isconfigured to flexibly support a seated user's thighs. For this reason,the seat cushion 170 includes an indentation 170A located slightlyforwardly of the seated user's hip joint (FIG. 12). The upholsterycovering the seat cushion 170B includes a tuck or fold at theindentation 170A to allow the material to expand or stretch duringdownward flexing of the thigh support region since this results in astretching or expanding at the indentation due to the fact that the topsurface of the upholstery is spaced above the hinge axis of flexure ofthe seat shell 164. Alternatively, a stretch fabric or separated frontand rear upholstered cushions can be used.

Seat Passive/Flexible Thigh Support (without Gas Spring)

[0102] A passive thigh flex device 237 (FIG. 30) includes a reinforcingplate 238 attached to the underside of the thigh-supporting frontportion 166 of seat shell 164 (FIG. 4B). A pair of L-shaped stop tabs239 (FIG. 29) are bent downwardly from the body of the plate 238. TheL-shaped tabs 239 include horizontal fingers 240 that extend rearwardlyto a position where the fingers 240 overlap a front edge 241 of the seatframe 163. Bushings 242 are positioned inside the L-shaped tabs 239 andinclude a notch 243 engaging the front edge 241. A curvilinearly-shapedleaf spring 244 is positioned transversely under the reinforcing plate238 with the ends 245 of the leaf spring 244 engaging recesses in thetop of the bushings 242. The leaf spring 244 has a curvilinear shape sothat it is in compression when in the present passive thigh flex device237. When a seated user presses downwardly on the thigh-supporting frontportion 166 with his/her thighs, the leaf spring 244 bends in the middlecausing the reinforcing plate 238 to move toward the front edge 241 ofthe seat frame 163. When this occurs, the fingers 240 each move awayfrom their respective bushings 242 (FIG. 31). When the seated userreleases the downward pressure on the thigh-supporting front portion166, the spring 244 flexes toward its natural bent shape causing thebushings 242 to move back into engagement with the fingers 240 (FIG.30). Notably, this passive thigh flex device 237 allows the user to flexthe lateral sides of the thigh-supporting front portion 166 of the seatshell 164 independently or simultaneously. The degree of flexure of thepassive thigh flex device 237 is limited by the distance that bushings242 can be moved in L-shaped tabs 239.

[0103] In the foregoing description, it will be readily appreciated bythose skilled in the art that modifications may be made to the inventionwithout departing from the concepts disclosed herein. Such modificationsare to be considered as included in the following claims, unless theseclaims by their language expressly state otherwise.

The invention claimed is:
 1. A seating unit comprising: a base assemblyincluding a seat-supporting structure; a seat supported on the baseassembly; a back frame pivoted to the base assembly for movement betweenupright and reclined positions; a compliant back connected to the backframe in at least one top connection and to one of the back frame andthe seat at bottom connections vertically spaced from the at least onetop connection, the bottom connections being located proximate a rear ofthe seat and in front of a bottom of the compliant back so that thebottom connections define an axis that is adapted to be generallyaligned with an area associated with a seated user's hip bone and lowerspine, the compliant back being flexible so that the compliant backundergoes controlled flexure between the top and bottom connections uponflexure of a seated user's back; and the seat having a front portionslidably supported on the seat-supporting structure of the base assemblyand a rear portion pivotably connected to the back frame so that theseat moves forwardly in a synchronized motion with the back frame duringrecline of the back frame.
 2. The seating unit defined in claim 1wherein the compliant back includes upper and lower sections operablyconnected together for counter-rotational movement, the upper sectionbeing pivoted to the back frame at the top connection and the lowersection including forwardly-extending flanges pivoted to the back frameat the bottom connections, a rearward distance from the bottomconnections to a lower front surface of the lower section adapted to beabout equal to a predetermined distance calculated from an averageseated user's hip joint to the average seated user's rear/lower spinebones, so that the compliant back is adapted to flex and simultaneouslyprovide comfortable postural support upon flexure of the seated user'slower back.
 3. The seating unit defined in claim 1 wherein the compliantback includes a back shell having upper and lower stiff sectionsconnected by a flexible zone adapted to be located generally in a lumbararea of a seated user.
 4. The seating unit defined in claim 3 whereinthe flexible zone includes a plurality of horizontal slits extendinggenerally across the compliant back but terminating to leave anuninterrupted band of material at opposite side edges of the lumbararea.
 5. The seating unit defined in claim 4 including a torsionallumbar support mechanism operably attached to the back shell, thetorsional lumbar support mechanism biasing the shell toward aforwardly-protruding convex shape for optimal lumbar support.
 6. Theseating unit defined in claim 5 wherein the compliant back includes aback shell, and including a vertically-adjustable lumbar supportattached to the back shell of the compliant back for vertical adjustmentto change a shape of a front surface of the compliant back in the lumbararea of the seated user.
 7. The seating unit defined in claim 6 whereinthe vertically-adjustable lumbar support includes laterally extendinghandles constructed to engage and track with a perimeter edge of thecompliant back and constructed to slidably engage thevertically-adjustable lumbar support to permit the handles to adjust inand out to follow the perimeter edge.
 8. The seating unit defined inclaim 1 including a torsional lumbar support mechanism attached to oneof the bottom connections for biasing the compliant back toward aforwardly-protruding convex shape.
 9. The seating unit defined in claim1 wherein the compliant back includes a back shell, and including avertically-adjustable lumbar support operably attached to a frontsurface of the back shell of the compliant back, thevertically-adjustable lumbar support being configured to change a forceof support at the front surface of the compliant back in a lumbar areaof a seated user.
 10. The seating unit defined in claim 9 including atleast one handle that slidably engages the vertically-adjustable lumbarsupport in a generally horizontal direction, the handle being configuredto follow along a perimeter edge of the compliant back for verticallyadjusting the vertically-adjustable lumbar support.
 11. The seating unitdefined in claim 1 wherein the top connection includes a top pivotconnection.
 12. The seating unit defined in claim 11 wherein the toppivot connection includes a protruding T-shaped connector on the backframe and a mating recess in the compliant back, the recess beingconfigured to receive and frictionally engage the T-shaped protrudingconnector to attach the compliant back to the back frame.
 13. Theseating unit defined in claim 1 wherein the compliant back includes abelt bracket attached along a bottom edge of the compliant back, thebelt bracket including flanges defining a part of the bottom connectors.14. The seating unit defined in claim 13 including an adjustabletorsional lumbar support mechanism attached to one of the bottomconnectors.
 15. The seating unit defined in claim 1 wherein the backframe defines an inverted curvilinear arch.
 16. The seating unit definedin claim 1 wherein the back frame includes an internal metalreinforcement and an exterior polymeric covering that covers all sidesof an intermediate section of the internal metal reinforcement.
 17. Theseating unit defined in claim 1 wherein the back frame includesconfigured ends positioned on opposing sides of the rear portion of theseat, the configured ends defining first pivots for pivotal connectionto the back frame and second pivots for pivotal connection to the seat.18. A seating unit comprising: a base assembly; a back frame pivoted tothe base assembly for movement between upright and reclined positions;and a compliant back operably attached to the back frame at a topconnection and operably attached to the back frame at bottomconnections, the compliant back including a forwardly-extending flangegenerally located along its lower edge forming an axis of rotation atthe bottom connections, the axis being located proximate a rear sectionof the seat and in front of the compliant back, the compliant backincluding a thoracic portion, a pelvic portion, and a flexible lumbarportion constructed so that when a seated user flexes his/her lower backrearwardly, a pelvic portion of the compliant back moves pivotallydownwardly and rearwardly about the axis, the lumbar portion of thecompliant back flexibly moves generally rearwardly to form a more planararrangement with the pelvic portion, and a thoracic portion of the backpivots about the top connection, whereby the compliant back, incombination with the back frame and base assembly, is adapted to providepostural support for a seated user's back that is comfortable and yetposturally supports significant flexing and moving of the seated user'storso and spine.
 19. The seating unit defined in claim 18 including anadjustable torsional lumbar support spring mechanism attached to thecompliant back for adjustably torsionally biasing the compliant back toa forwardly-protruding convex shape for optimal lumbar support for theseated user.
 20. The seating unit defined in claim 19 wherein thecompliant back includes a molded shell having a resilient lumbarsection.
 21. The seating unit defined in claim 20 including a beltbracket attached to a bottom edge of the molded shell.
 22. The seatingunit defined in claim 21 wherein the compliant back includes a backshell, and including a vertically-adjustable lumbar support operablyattached to a front of the back shell of the compliant back.
 23. Theseating unit defined in claim 18 wherein the top connection includes aprotrusion on the base frame and a mating recess on the compliant back,the recess being configured to receive and frictionally engage theprotrusion.
 24. The seating unit defined in claim 18 wherein thecompliant back includes a back shell, and including avertically-adjustable lumbar support attached to the back shell of thecompliant back in a lumbar area of the seated user, for changing a shapeof a front surface of the compliant back in the lumbar area.
 25. Theseating unit defined in claim 24 including handles operably engaging thevertically-adjustable lumbar support and configured to follow aperimeter edge of the compliant back during vertical adjustment of thevertically-adjustable lumbar support.
 26. The seating unit defined inclaim 25 wherein the back frame has configured ends positioned onopposite sides of the compliant back, the configured ends defining aback-tilt axis, a seat-tilt axis, and a back-shell bottom-tilt axis thatis located rearwardly of the back-tilt axis and the seat-tilt axis. 27.The seating unit defined in claim 18 wherein the compliant back includesa covering sheet, at least a stretchable portion of which is stretchablematerial for maintaining the covering sheet in tension on the compliantback during flexure of the compliant back.
 28. The seating unit definedin claim 27 wherein the stretchable portion includes a strip of stretchfabric sewn to a lower edge of the covering sheet.
 29. The seating unitdefined in claim 28 wherein the compliant back includes a back shell,and includes an extrusion attached to the strip of stretch fabric, theextrusion being secured to a lower edge of the back shell.
 30. Theseating unit defined in claim 29 wherein the extrusion includes a notchfor receiving an edge of the strip of stretch fabric and is sewn to thestrip of stretch fabric along the notch.
 31. The seating unit defined inclaim 18, wherein the bottom connections include an aperture on thecompliant back and an aperture-engaging pivot member on the back frame.32. In a seating unit having a base, a seat, a back frame rotatablyattached to the base, and a first energy mechanism operably connected tothe back frame and the base for biasing the back frame toward an uprightposition, the improvement comprising: a compliant back that is flexiblybendable to define different curvilinear shapes for sympatheticallysupporting a seated user's back, and a belt bracket withforwardly-extending flanges pivotally connecting the compliant back tothe back frame at a first connection, the compliant back including asecond connection pivotally connecting the compliant back to the backframe at a second location spaced vertically from the first connection,such that the compliant back is constrained to move over a range limitedby the first and second connections; and a second energy mechanismincluding a force generating mechanism located generally at one of thefirst and second connections and constructed to bias the bracket and soas to bias a lumbar portion of the compliant back forward with respectto the seating unit.
 33. The seating unit defined in claim 32 whereinthe belt bracket includes side flanges positioning the first connectiongenerally at a rear of the seating unit's seat at a location where thefirst connection is adapted to be generally aligned with a pelvic boneof a typical seated user so that, when the seated user flexes his/herlower back rearwardly, a pelvic portion of the back moves downwardly andrearwardly, a lumbar portion of the back moves generally flexiblyrearwardly to form a more planar arrangement with the pelvic portion,and a thoracic portion of the back pivots about the second connection,the pelvic portion and the thoracic portion being flexiblyinterconnected by the lumbar portion and adapted to move in a mannersympathetic to movements of the seated user's back.
 34. A seating unitconstruction comprising: a base assembly; a seat; a back frame pivotedto the base assembly for movement between upright and reclinedpositions; and a compliant back pivoted to the back frame at a fixed topconnection and including forwardly-extending flanges pivoted to one ofthe back frame, the seat, and the base assembly at bottom connections,the bottom connections being spaced forwardly from a lower front centralsurface of the compliant back, whereby, upon flexure of a seated user'sspine and lower back, the compliant back is adapted to flexsympathetically and follow flexure of the seated user's back and spine.35. The seating unit construction defined in claim 34 wherein the bottomconnections connect the flanges of the compliant back to the back frame.36. The seating unit construction defined in claim 35 wherein thecompliant back comprises relatively stiff upper and lower sectionsinterconnected by a flexible section.
 37. A seating unit comprising: abase assembly; a seat; an inverted U-shaped back frame having anintermediate top section and a pair of configured end sections pivotedto the base assembly, a T-shaped top connector protruding from the topsection and a pair of bottom connectors in the configured end sections;a compliant back including a top recess configured to receive andfrictionally engage the top connector, and further including a beltbracket along a lower edge with opposing flanges that extend forwardly adistance for connection to the bottom connectors; and a connectingmechanism pivotally connecting the opposing flanges to the bottomconnectors at a location proximate a rear of the seat.
 38. The seatingunit defined in claim 37 wherein the compliant back includes a flexiblelumbar section, and wherein the distance that the flanges extendforwardly is a few inches so that the distance is calculated to be aboutequal to a distance from a hip joint of a seated user to a lower spinebone of the average seated user, such that the compliant back, whenflexed, flexes in a sympathetic manner that provides continuous andcomfortable support to a seated user's spine.
 39. A back constructionfor a seating unit comprising: a back frame; a compliant back having aforwardly-protruding lumbar support section that is characteristicallyflexible and bendable, such that the compliant back can be flexed to aplurality of different convex shapes; top and bottom connectionspivotally connecting the compliant back to the back frame; and anadjustable force-generating mechanism operably attached to at least oneof the compliant back and the back frame, the force-generating mechanismbeing constructed to provide an adjustable biasing force that adjustablybiases the lumbar support section forwardly for optimal lumbar supportfor a seated user's back, but the force-generating mechanismcharacteristically providing the biasing force without forcing a shapechange in the compliant back.
 40. A back construction for a seating unitcomprising: a back frame; a compliant back having a forwardly-protrudinglumbar support section that is flexibly movable to a plurality ofdifferent convex shapes, with each shape being adapted to providepostural and comfortable support to a back of a seated user; top andbottom connections pivotally connecting the compliant back to the backframe; and an adjustable torsional force-generating mechanism operablyattached to one or both of the compliant back and the back frame to biasthe lumbar section forwardly for optimal lumbar support for the seateduser's back, the torsional force-generating mechanism being operablymounted at the bottom connection to the back frame and the compliantback.
 41. The back construction defined in claim 40 wherein thecompliant back includes a relatively stiff thoracic support section anda relatively stiff pelvic support section, which are interconnected bythe lumbar support section.
 42. The back construction defined in claim41 wherein the lumbar support section comprises a flexible sheet ofmaterial.
 43. The back construction defined in claim 40 whereintorsional force-generating mechanism includes a spring and a handle, thehandle being rotatable to wind and unwind to adjust a tension of thespring, the spring being operably connected between the compliant backand the back frame to bias the lumbar support section of the compliantback toward a forwardly convex shape.
 44. The back construction definedin claim 43 wherein the torsional force-generating mechanism includes alever to provide mechanical advantage when adjusting the tension of thespring.
 45. A seating unit comprising: a base assembly including acontrol housing having an energy source therein; a seat on the baseassembly; a back support operably interconnected to the energy sourcefor movement between an upright position and a reclined position, theback support including a back frame and a back shell, the back shellcomprising a resiliently flexible polymeric sheet shaped to and adaptedto support a back of a seated user, with a semi-rigid lower areadisposed generally in a pelvic area on the seating unit, a flexiblecentral area disposed above the lower area and generally in a lumbararea on the seating unit, and a semi-rigid upper area disposed above thecentral area in a thoracic area on the seating unit; the back framehaving a first attachment coupling the upper area of the back shell tothe back frame, and a plurality of pivotal second attachments forpivotally coupling the lower area of the back shell to the back frame,the second attachments constraining movement of the lower area to forceflexure to occur in a controlled sympathetic manner in the lumbar areain order to adapt the back support to assure continuous and comfortablesupport of the seated user's spine in the lumbar area during flexure ofthe seated user's spine while seated, the central area of the back shellcomprising a plurality of vertically spaced apart slots in the sheetextending generally horizontally across a portion of the central area ofthe back support, the slots terminating prior to the perimeter edge ofthe sheet, whereby the slots define a plurality of elongated horizontalresilient straps in the central area, each of the straps beingdimensioned and adapted to provide resilient support for the seated userwhen sitting on the seating unit; and the lower area of the back shellincluding a reinforcement having forward extending flanges pivotallycoupled to the second attachments of the back frame, the reinforcementand pivotal attachment being adapted to provide movable firm support forat least a portion of the pelvic area of the seated user.
 46. Theseating unit defined in claim 45 wherein the back frame includes a firstpivot and the back frame is pivotally attached to the base assembly formovement of the back support between the upright and reclined positions,with the first pivot approximately coinciding with an axis located at arear of the seat so that the axis is adapted to be located generally ata hip joint of the seated user.
 47. The seating unit defined in claim 45wherein the the back frame comprises an internal metal reinforcementencased in a resilient polymeric covering.
 48. The seating unit definedin claim 45 including a seat operably mounted on the base assembly, theseat forming a link interconnecting the back support to the energysource.
 49. A seating unit comprising: a base assembly including acontrol housing having an energy source therein; a seat on the baseassembly; a back support operably interconnected to the energy sourcefor movement between an upright position and a reclined position, theback support including a back frame and a back shell, the back shellcomprising a resiliently flexible polymeric sheet shaped to and adaptedto support a back of a seated user, with a semi-rigid lower areadisposed generally in a pelvic area on the seating unit, a flexiblecentral area disposed above the lower area and generally in a lumbararea on the seating unit, and a semi-rigid upper area disposed above thecentral area in a thoracic area on the seating unit; the back framehaving a first attachment coupling the upper area of the back shell tothe back frame, and a plurality of pivotal second attachments forpivotally coupling the lower area of the the back shell to the backframe, the second attachments constraining movement of the lower area toforce flexure to occur in a controlled sympathetic manner in the lumbararea in order to adapt the back support to assure continuous andcomfortable support of the seated user's spine in the lumbar area duringflexure of the seated user's spine while seated, the central area of theback shell comprising a plurality of vertically spaced apart slots inthe sheet extending generally horizontally across a portion of thecentral area of the back support, the slots terminating prior to theperimeter edge of the sheet, whereby the the slots define a plurality ofelongated horizontal resilient straps in the central area, each of thestraps being adapted and dimensioned so as to provide resilient supportfor the seated user when sitting on the seating unit; and the lower areaof the back shell including a reinforcement having forward extendingflanges pivotally coupled to the second attachments of the back frame,the reinforcement and pivotal attachment being adapted to providemovable firm support for at least a portion of the pelvic area of theseated user, the pivotal second attachments for pivotally coupling thelower area of the the back shell to the back frame including a biasingdevice that biases the central area of the back shell in a forwarddirection.
 50. The seating unit defined in claim 49 wherein the thelower area of the the back shell includes forward extending flangespivotally coupled to the second attachments of the back frame and thebiasing device includes a torsion spring operably interconnected to theforward extending flanges.
 51. The seating unit defined in claim 50wherein the the biasing device includes means for adjusting thepretension on the torsion spring.
 52. A seating unit comprising: a baseassembly including a control housing having an energy source therein; aseat on the base assembly; a back support operably interconnected to theenergy source for movement between an upright position and a reclinedposition, the back support including a back frame and a back shell, theback shell comprising a resiliently flexible polymeric sheet shaped toand adapted to support a back of a seated user, with a semi-rigid lowerarea disposed generally in a pelvic area on the seating unit, a flexiblecentral area disposed above the lower area and generally in a lumbararea on the seating unit, and a semi-rigid upper area disposed above thecentral area and in a thoracic area on the seating unit; and the backframe having a first attachment coupling the upper area of the backshell to the back frame, and a plurality of pivotal second attachmentsfor pivotally coupling the lower area of the the back shell to the backframe, the second attachments constraining movement of the lower area toforce flexure to occur in a controlled sympathetic manner in the lumbararea in order to adapt the back support to assure continuous andcomfortable support of the seated user's spine in the lumbar area duringflexure of the seated user's spine while seated, the lower area of theback shell including forward extending flanges forming an axis ofrotation at the pivotal second attachments of the back frame, the axisof rotation being located at or rearward of a rear of the seat so thatthe axis is generally adapted for location proximate a seated user'spelvic bone so that when the seated user flexes his/her lower backrearwardly, the lower portion of the back shell moves downwardly andrearwardly, and the central portion of the back shell flexes generallyrearwardly to form a more planar arrangement with the lower portion. 53.A seating unit comprising: a base assembly including a control housinghaving an energy source therein; a seat on the base assembly; a backsupport operably interconnected to the energy source for movementbetween an upright position and a reclined position, the back supportincluding a back frame and a back shell, the back shell comprising aresiliently flexible polymeric sheet shaped to and adapted to support aback of a seated user, with a semi-rigid lower area disposed generallyin a pelvic area on the seating unit, a flexible central area disposedabove the lower area and generally in a lumbar area on the seating unit,and a semi-rigid upper area disposed above the central area andgenerally in a thoracic area on the seating unit; and the back framehaving a first attachment coupling the upper area of the back shell tothe back frame, and a plurality of pivotal second attachments forpivotally coupling the lower area of the the back shell to the backframe, the second attachments constraining movement of the lower area toforce flexure to occur in a controlled sympathetic manner in the lumbararea in order to adapt the back support to assure continuous andcomfortable support of the seated user's spine in the lumbar area duringflexure of the seated user's spine while seated, the back frame defininga curvilinear arch.
 54. A seating unit comprising: a base assemblyincluding a control housing having an energy source therein; and a backassembly movably supported on the back assembly and including a backsupport operably interconnected to the energy source, the back supportincluding a back frame and a back shell connected to the back frame byat least one connection, the back shell comprising a resilientlyflexible polymeric sheet adapted to support a back of a seated user, thesheet including a lower area disposed generally in a pelvic area on theseating unit, a central area disposed above the lower area and generallyin a lumbar area on the seating unit, and an upper area disposed abovethe central area and generally in a thoracic area on the seating unit; acushion on a forward face of the back shell; and a vertically adjustablelumbar support located in front of the back shell, the lumbar supportbeing movably supported on the back support and configured for verticaladjustment to change a shape of a front surface of the back in thelumbar area, the vertically adjustable lumbar support includinglaterally extending handles constructed to engage and follow configurednon-parallel opposing perimeter edges of the back shell and constructedto slidably engage the vertically adjustable lumbar support to permitthe handles to adjust laterally in and out to follow the perimeteredges.
 55. A seating unit comprising: a base assembly; a seat supportedon the base assembly; a back frame pivoted to the base assembly formovement between upright and reclined working positions; a compliantback pivotally connected to the back frame in at least one topconnection and pivotally connected to one of the back frame and the seatat bottom connections vertically spaced from the at least one topconnection, the bottom connections being located proximate a rear of theseat and in front of a bottom of the compliant back so that the bottomconnections define an axis at a rear of the seat that is adapted to begenerally aligned with a seated user's hip bone, the compliant backhaving a stiff thoracic section and a stiff pelvic section, the lumbarsection being characteristically flexible in a horizontal direction,such that the compliant back can be easily flexed to provide differentshapes for optimal lumbar support, but the lumbar section beingsubstantially incompressible in directions toward the thoracic andpelvic sections so that the lumbar section causes the thoracic andpelvic sections to pivot along predetermined paths about the top andbottom connections when the lumbar section is flexed, such that thecompliant back undergoes controlled flexure between the top and bottomconnections upon flexure of the lumbar section caused by flexure of aseated user's back; and the seat being operably supported on the baseassembly to move in a synchronized angular motion with the back frameduring recline of the back frame.
 56. The seating unit defined in claim55 including a biasing device biasing the compliant back to a shape inwhich the lumbar section protrudes forwardly, the biasing devicecharacteristically providing a biasing force but not forcing a shapechange in the compliant back.
 57. The seating unit defined in claim 55wherein the back frame is pivoted to the base assembly for movementabout a back tilt axis, and the seat is pivoted to the back frame formovement about a seat tilt axis, the back tilt axis and the seat tiltaxis being arranged and the back and the seat being operably coupled toprovide a synchronous movement during recline of the back frame.
 58. Aseating unit comprising: a base assembly; a back frame pivoted to thebase assembly for movement between upright and reclined workingpositions; and a compliant back operably attached to the back frame at atop connection and operably attached to the back frame at bottomconnections, the compliant back including a stiff thoracic portion and astiff pelvic portion connected by a flexible lumbar portion, the bottomconnections being forward of the pelvic portion and above the seat, thetop and bottom connections and thoracic, pelvic, and lumbar portionsbeing constructed so that when a seated user flexes his/her lower backrearwardly, the pelvic portion of the compliant back moves pivotallydownwardly and rearwardly, the lumbar portion of the compliant backflexibly moves generally rearwardly to form a more planar arrangementwith the pelvic portion, and the thoracic portion of the back pivotsabout the top connection, whereby the compliant back, in combinationwith the back frame and base assembly, is adapted to provide posturalsupport for a seated user's back that is comfortable and yet posturallysupports significant flexing and moving of the seated user's torso andspine.
 59. A seating unit comprising: a base assembly; a seat operablysupported on the base assembly; a back frame pivoted to the baseassembly for movement between upright and reclined working positions;and a compliant back operably attached to the back frame at a topconnection and operably attached to one of the seat and the back frameat bottom connections, the compliant back including a stiff thoracicportion and a stiff pelvic portion connected by a flexible lumbarportion, the bottom connections being forward of the pelvic portion andabove the seat, the top and bottom connections and thoracic, pelvic, andlumbar portions being constructed so that when a seated user flexeshis/her lower back rearwardly, the pelvic portion of the compliant backmoves pivotally downwardly and rearwardly, the lumbar portion of thecompliant back flexibly moves generally rearwardly to form a more planararrangement with the pelvic portion, and the thoracic portion of theback pivots about the top connection, whereby the compliant back, incombination with the back frame and base assembly, is adapted to providepostural support for a seated user's back that is comfortable and yetposturally supports significant flexing and moving of the seated user'storso and spine.
 60. The seating unit defined in claim 1, wherein thebase assembly includes castors adapted to rollingly engage a floorsurface, and wherein the base assembly, the back frame and the seatdefine a mobile task chair.
 61. The seating unit defined in claim 18,including a seat, and wherein the base assembly includes castors adaptedto rollingly engage a floor surface, and wherein the base assembly, theback frame and the seat define a mobile task chair.
 62. The seating unitdefined in claim 32, wherein the base includes castors adapted torollingly engage a floor surface, and wherein the base assembly, theback frame, and the seat define a mobile task chair.
 63. The seatingunit defined in claim 34, wherein the base assembly includes castorsadapted to rollingly engage a floor surface, and wherein the baseassembly, the back frame and the seat define a mobile task chair. 64.The seating unit defined in claim 37, wherein the base assembly includescastors adapted to rollingly engage a floor surface, and wherein thebase assembly, the back frame and the seat define a mobile task chair.65. The seating unit defined in claim 45, wherein the base assemblyincludes castors adapted to rollingly engage a floor surface, andwherein the base assembly, the back frame and the seat define a mobiletask chair.
 66. The seating unit defined in claim 49, wherein the baseassembly includes castors adapted to rollingly engage a floor surface,and wherein the base assembly, the back frame and the seat define amobile task chair.
 67. The seating unit defined in claim 52, wherein thebase assembly includes castors adapted to rollingly engage a floorsurface, and wherein the base assembly, the back frame and the seatdefine a mobile task chair.
 68. The seating unit defined in claim 53,wherein the base assembly includes castors adapted to rollingly engage afloor surface, and wherein the base assembly, the back frame and theseat define a mobile task chair.
 69. The seating unit defined in claim54, wherein the base assembly includes castors adapted to rollinglyengage a floor surface, and wherein the base assembly, the back frameand the seat define a mobile task chair.
 70. The seating unit defined inclaim 55, wherein the base assembly includes castors adapted torollingly engage a floor surface, and wherein the base assembly, theback frame and the seat define a mobile task chair.
 71. The seating unitdefined in claim 58, including a seat, and wherein the base assemblyincludes castors adapted to rollingly engage a floor surface, andwherein the base assembly, the back frame and the seat define a mobiletask chair.
 72. The seating unit defined in claim 59, wherein the baseassembly includes castors adapted to rollingly engage a floor surface,and wherein the base assembly, the back frame and the seat define amobile task chair.